Case Study Food Process Refrigeration Milk Chilling

A milk storage tank has been successfully converted from R22 to R407C, an HFC with expected long term availability into the future. The system comprised of two bulk storage tanks fitted with two refrigeration units running in parallel. The units used Prestcold compressors with air cooled condensers. One system was converted to R407C while the other was left running on R22 for reference. The retrofit was carried out using the now well documented procedure for converting to R134a. The original mineral oil was removed and replaced with a POE oil of equivalent viscosity. Filter drier cores and seals were changed to those compatible with R134a. The system was then run for a number of hours before removing the oil and replacing it with a fresh charge of POE oil. This procedure was repeated until the concentration of mineral oil in the POE oil fell below 1% (3 flushes). The R22 was removed from the system and the R407c was added in the liquid phase.The converted chiller was able to pull down the temperature of the milk in the tank faster than the R22 reference indicating a large refrigerating capacity. It also maintained lower milk temperatures once an equilibrium temperature had been reached. With power consumption also being slightly higher, the COPs of the two systems were very similar. It is worth noting that the discharge temperature of the R407C system was around 15°C lower than the R22 system. Several months of trouble free operation have now been experienced.

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